I just received a few-dozen-gigabyte squashfs that contains a PostgreSQL database. In order to be able to conveniently query it, I need to have a write access, which makes it complicated. Is there a filesystem similar to (or a setting for) overlayfs/autofs that would enable this use case? I'm getting the impression that when I ran select * from tbl limit 1;, overlayfs was trying to rewrite the whole file, which is not acceptable in my situation.

  • Odd that it needs to write. Have you tried default_transaction_read_only = on; in your PostgreSQL config? Also, move the WAL logs—they may need to be writable. – derobert Jan 28 '16 at 18:31
  • @derobert: And pidfile? – d33tah Jan 28 '16 at 18:42
  • Yeah, though that's tiny so you could just let overlay etc. take care of that. I'm not sure if pg can actually run w/o writing to the data files.. Also, any reason for it to be a squashfs? Could it be something typically writable like ext4 instead? – derobert Jan 28 '16 at 18:44
  • @derobert: this is what I have basically. – d33tah Jan 28 '16 at 18:45

You could take a look at the project squashmount. It mounts a directory with both a squashfs and an autofs/overlay/overlayfs system to allow for squashing ro access as well as write access. Completely configurable on how much change requires re-squashing, its a nice to use for database storage, repos spools, etc.

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